Transfection by cationic gemini lipids and surfactants

Abstract

Diseases that are linked to defective genes or mutations can in principle be cured by gene therapy, in which damaged or absent genes are either repaired or replaced by new DNA in the nucleus of the cell. Related to this, disorders associated with elevated protein expression levels can be treated by RNA interference via the delivery of siRNA to the cytoplasm of cells. Polynucleotides can be brought into cells by viruses, but this is not without risk for the patient. Alternatively, DNA and RNA can be delivered by transfection, i.e. by non-viral vector systems such as cationic surfactants, which are also referred to as cationic lipids. In this review, recent progress on cationic lipids as transfection vectors will be discussed, with special emphasis on geminis, surfactants with 2 head groups and 2 tails connected by a spacer.

Fig. 1. Schematic representation of the RNAi (RNA interference) strategy. Left, the DNA of a gene is transcribed in the nucleus to mRNA (messenger RNA) and then translated into a protein in the ribosome; right, antisense RNA derived from siRNA (small interfering RNA) is bound to the RNA-induced silencing complex together with the complementary mRNA, leading to degradation of the latter.

Chart 1. (Pseudo)glyceryl (A) and related lipids (B and C).

Fig. 2. Steps and barriers to overcome in gene delivery with non-viral vectors:, 1) complexation and condensation of the polynucleic acid by the cationic lipid into a lipoplex, 2) electrostatic attraction to the cell surface, 3) uptake by endocytosis, 4) degradation in a lysosome or 5) escape from the endosome, 6) entry into the nucleus, 7) expression as a protein, and 8) therapeutic effect.

Chart 2. Alternative hydrophobic tails.

Chart 3. Multivalent cationic lipids.

Chart 4. Bola-amphiphiles for transfection.

Scheme 1. A) Oxidative dimerization of an amphiphilic thiol into a disulfide gemini surfactant. B) Reducible transfection agents.

Chart 5. Gemini: A and B, general cationic gemini structure, connected at the head (A) or in the linker region (B); C, natural gemini (cardiolipin, 22a) and cationic cardiolipin analogue 22b.

Chart 6. Quaternary ammonium geminis with alkyl spacer.

Chart 7. Quaternary ammonium geminis with other spacers.

Chart 8. Carbohydrate classical and gemini transfectants.

Chart 9. Geminis with multivalent head groups.

Chart 10. Transfectants with delocalized positive charge.

Chart 11. Headgroups with delocalized charge, A) and C) pyridinium resp. imidazolium geminis; B) pseudogeminis.

Chart 12. Amino acid-based gemini surfactants. Links between Lys in peptides are α unless otherwise indicated.

Chart 13. Geminis with chiral spacers.

Scheme 2. Lipidoids from A) acrylates, B) epoxides, C) rings.

Mark Damen, Alexander J. J. Groenen, Stijn van Dongen, Roeland J. M. Nolte, Bob J. Scholte and Martin C. Feiters